Peroxynitirite　(ONOO-)　is　a　potent　cytotoxin,　and　it　can　damage　tryptophan,　tyrosine　and　other　biomolecules.　The　kinetics　of　tryptophan　damaged　by　peroxynitrite　was　studied　by　stopped-flow　spectrophotometer　at　25　degrees　C.　When　peroxynitrite　is　present　in　excess,　there　are　many　products　formed　including　nitrotryptophan,　hydroxytryptohan,　N-formylkinurenine　or　dihydroxytryptophan,　oxindole,　and　hydropyrroloindole.　The　kinetics　of　tryptophan　loss　can　represent　the　kinetics　of　peroxynitrite　damaging　tryptophan　as　a　whole.　The　kinetics　of　this　reaciotn　was　studied　by　monitoring　the　decrease　of　fluorescence　of　tryptophan,　and　the　apparrent　second　order　rate,　2.85　x　104　M-1　s(-1),　and　the　apparent　activation　energy,　39.4　KJ-mol(-1)　are　derived.